On Fertile Ground [Anglais] [Broché]

Not surprisingly, Ellison spends a considerable amount of time describing the results of his own extended fieldwork among Efe hunter-gatherers and Lese horticulturalists living in the rainforests of the Democratic Republic of Congo. This work has been innovative in bringing modern endocrinologic methods into anthropologic field studies. Ellison has also been involved in similar projects in other parts of the world, and the results of those projects receive attention as well. At the same time, he provides a broad overview of a wide range of work in demography, epidemiology, anthropology, and basic reproductive biology. And he weaves all these disparate lines of research together to provide an integrated picture of female reproductive cycles, pregnancy and pregnancy loss, parturition, lactation and lactational infecundability, reproductive maturation, spermatogenesis, the effects of energy balance on reproduction, and reproductive senescence (with special emphasis on the evolution of menopause). As this list suggests, much of the focus is on female physiology. Males get fewer than 30 pages of their own. In part, this focus reflects the author's own research interests, but it can also be justified on evolutionary grounds. As Ellison makes clear, the physiologic burdens of childbearing are vastly greater for women than for men. Consequently, natural selection has had more work to do over the course of human history and prehistory to reconcile female reproductive effort with limited local resources, especially food resources. Male reproduction is cheap by comparison in terms of energy cost.

Ellison argues convincingly that an evolutionary approach to reproduction is essential, but he does not always convey just how hard it is to apply such an approach convincingly. Good laboratory work is relatively easy to do; good fieldwork is much more difficult. And it is vastly more difficult to make a convincing case out of the sorts of cross-population and cross-species comparisons that are the foundations of inference about evolution. As researchers progress from one type of study to the next in this sequence, it becomes more and more difficult to maintain control and replicability. Evolutionary studies, in particular, often involve arguments about plausibility and ex post facto reasoning. It is not that any thinking biologist doubts that the human reproductive process evolved by natural selection; the problem, rather, is one of providing critical tests of particular evolutionary hypotheses.

Ellison is brilliant at concocting plausible ecologic and evolutionary hypotheses (which is no mean feat). And he is usually fairly realistic about the difficulties involved in testing them (his discussion of the evolution of menstruation in hominids is a good example). But occasionally, he treats his own speculations as if they were established science. For example, many physiologists will find his arguments about the mechanisms involved in parturition and lactational anovulation to be controversial (to say the least), and demographers are sure to howl over his assertion that social factors are generally unimportant as immediate causes of variation in human fertility. But even if most researchers will not yet be ready to go as far as Ellison on many of these issues, his forceful arguments are sure to inspire the difficult empirical work that is needed in order to support or refute them.

Ellison's writing is consistently graceful, cogent, and clear. His five-page overview of the basic logic of hormones, receptors, and transport proteins, written for the general reader, is one of the most elegant I have ever read. Occasionally, it might have been useful to supplement his prose with diagrams and figures, but for the most part he shows just how effective English can be as a medium for scientific expression -- something that cannot be said of most science writing.

In sum, Ellison's book is a thought provoker and occasionally an objection provoker. It is brimming with ideas, many of them conjectural but all of them stimulating. It should be read not as a catalogue of established scientific knowledge but as an intellectual road map for future research on reproductive ecology. It deserves to set an agenda, even if many of its details ultimately turn out to be wrong.

James Wood, Ph.D.
Copyright © 2001 Massachusetts Medical Society. All rights reserved. The New England Journal of Medicine is a registered trademark of the MMS. --Ce texte fait référence à une édition épuisée ou non disponible de ce titre.